The present invention relates to a positive electrode activator used in the lithium secondary battery and a lithium secondary battery using said activator.
In recent years, the secondary battery is one of the indispensable components as a power supply for personal computers and cellular mobile telephones and as a power supply for electric cars and power storage.
Portable computers (including pen-based portables) and mobile computing equipment such as portable information terminals (personal digital assistant, personal intelligent communicator or hand-held communicator) are required to provide a compact configuration and light weight.
However, a high voltage is required because a great amount of power is consumed by the back light of the liquid crystal display panel, plotting control and a disk drive motor. Power capacity is currently obtained by increasing the number of batteries to be connected in series. For this reason, it is difficult at present to achieve a compact configuration and light weight of the system.
Furthermore, electric cars free of emission gas and noise are attracting keen interest as a result of rising awareness of the global environmental problem. However, electric cars requires voltage higher than 300 volts. This increases the number of batteries to be connected in series, giving rise to such problems as short traveling distance, poor acceleration properties, limited in-car space and poor car body stability.
Of the secondary batteries, especially the lithium secondary battery using non-aqueous electrolyte is attracting attention because it is expected to provide high voltage, light weight and high energy density.
For example, LixCoO2, etc. disclosed in the Official Gazette of Japanese Patent Laid-Open NO.136131/1980 provides an electromotive force of 3.6 to 3.8 volts or more for Li/Li(+), and is commonly used as a high energy density secondary battery positive electrode.
Furthermore, it is known that spinel based lithium manganate provides a high voltage of 4.6 to 4.7 volts when part of manganese is replaced with nickel (Journal of Electrochemical Society) 1994, Vol.141, P. 2,279).
The following two batteries are disclosed as lithium secondary batteries made of battery materials providing a high voltage in a similar manner; (1) a non-aqueous secondary battery made of spinel based lithium manganese multiple oxide (Official Gazette of Japanese Patent Laid-Open NO.073962/1999) represented by general formula LixMn(2xe2x88x92yxe2x88x92z)MYCrzO(4+p) (where M denotes Ni or Co) and having a potential of 4.5 volts or more for Li/Li (+). and (2) a lithium battery made of lithium inserted compound represented by general formula Lix+yMn(2xe2x88x92yxe2x88x92z)MzCrzO4 (where M denotes transition metal) and having a potential of 4.5 volts or more for Li/Li (+) (Official Gazette of Japanese Patent Laid-Open NO.147867/1997).
To improve stability at the time of charging and discharge, a lithium secondary battery s proposed in Official Gazette of Japanese Patent Laid-Open NO. 250119/1996 where charcogenide made up by replacing part of oxygen in the conventional metal oxide with a specified amount of a specific charcogen is used as a positive electrode activator instead of conventional metal oxide.
Spinel based lithium manganate formed by replacing part of manganese replaced with nickel, spinel based lithium manganese multiple oxide represented by general formula LixMn(2xe2x88x92yxe2x88x92z)MYCrzO(4+p) (where M denotes Ni or Co) and lithium inserted compound represented by general formula Lix+YMn(2xe2x88x92yxe2x88x92z)MzCrzO4 (where M denotes transition metal) provide the advantage of getting a high voltage of 4.5 to 4.7 volts. This makes it possible to reduce the number of batteries connected in series, thereby ensuring a compact configuration and light weight of the system.
However, only about 50 cycles of service life can be ensured according to evaluation of an enclosed type lithium secondary battery manufactured as a tentative product using these materials as a positive electrode.
The short cycle service life is attributable to the fact that organic component in electrolyte is easily if subjected to decomposition at a high voltage and is turned into vapor to be stored into the battery according to the prior art if charging and discharging of the enclosed lithium secondary battery are repeated at a high voltage of 4.5 to 4.7 volts. The stored gas not only interferes with electrochemical reaction by charging and discharging but also may cause the battery cylinder to expand and to explode in the final stage.
In the similar manner, the organic component is easily subjected to decomposition at a high voltage and is turned in to vapor to be stored in the battery easily, when using the electrolyte formed by dissolving LiPF6 having a density of one mol/liter into the mixed solvent of ethylene carbonate and dimethyl carbonate blended at a ratio of 1 to 2 disclosed in Official Gazette of Japanese Patent Laid-Open NO.073962/1999, or the electrolyte formed by dissolving LiBF4 having a density of 1.5 mol into the mixed solvent of ethylene carbonate and diethyl carbonate blended at a ratio of 30 to 70 disclosed in Official Gazette of Japanese Patent Laid-Open NO.147867/1997.
As described above, when charging and discharging of the enclosed lithium secondary battery is repeated at a high voltage according to the prior art, cycle life will exceed 500 cycles.
The object of the present invention is to provide a positive electrode activator for the lithium secondary battery and a lithium secondary battery using said activator, wherein said activator provides a high voltage and said battery ensures a service life of 500 cycles or more when designed in a enclosed battery structure.
The present invention relates the lithium secondary battery characterized in that charging termination voltage of the single battery is greater than 4.6 volts and smaller than 5.2 volts, and the average discharge voltage is greater than 4.3 volts and is smaller than 5.0 volts. The following summaries the present invention:
[1] A positive electrode activator for the lithium secondary battery composed of non-aqueous electrolyte including negative electrode, positive electrode and lithium salt; said positive electrode activator for secondary battery characterized by inclusion of the multiple oxide represented by a general formula Lix+aMn2xe2x88x92axe2x88x92bMbQcO4+d (where M denotes at least one element selected from among Ni, Fe, Co, Cu and Cr; Q denotes at least one element selected from among C, N, S, P, Si, F, Cl, I and Br; and x, a, b, c and d are within the range of 0xe2x89xa6xxe2x89xa61.1, 0xe2x89xa6axe2x89xa60.5, 0.05 xe2x89xa6bxe2x89xa61.0, 0.000001xe2x89xa6c  less than 0.05 and 0xe2x89xa6dxe2x89xa60.1, respectively).
[2] A positive electrode activator for the lithium secondary battery according to [1] wherein said positive electrode activator comprises (1) the multiple oxide represented by a general formula Lix+aMn2xe2x88x92axe2x88x92bMbQcO4+d (where M denotes at least one element selected from among Ni, Fe, Co, Cu and Cr+Q denotes at least one element selected from among C, N, S, P, Si, F, Cl, I and Br; and x, a, b, c and d are within the range of 0xe2x89xa6xxe2x89xa61.1, 0xe2x89xa6axe2x89xa60.5, 0.05 xe2x89xa6bxe2x89xa61.0,0.000001xe2x89xa6c less than 0.05 and 0xe2x89xa6dxe2x89xa60.1, respectively), and (2) the tilting function material where Q has a higher density on the surface layer than inside the particle.
[3] A positive electrode activator for the lithium secondary battery composed of non-aqueous electrolyte including negative electrode, positive electrode and lithium salt; said positive electrode activator characterized by inclusion of the multiple oxide represented by a general formula Lix+aMn2xe2x88x92axe2x88x92bMbQcO4+d (where M denotes at least one element selected from among Ni, Fe, Co, Cu and Cr; Q denotes at least one element selected from among C, N, S, P, Si, F, Cl, I and Br; and x, a, b, c and d are within the range of 0xe2x89xa6xxe2x89xa61.1, 0 xe2x89xa6axe2x89xa60.5, 0.05 xe2x89xa6bxe2x89xa61.0, 0.000001xe2x89xa6c less than 0.05 and 0xe2x89xa6dxe2x89xa60.1, respectively).
[4] A positive electrode activator for the lithium secondary battery according to [3] wherein said positive electrode activator further characterized by containing a tilting function material where Q of the multiple oxide has a higher density on the surface layer than inside the particle; said multiple oxide being represented by a general formula Lix+aMn2xe2x88x92axe2x88x92bMbQcO4+d (where M denotes at least one element selected from among Ni, Fe, Co, Cu and Cr; Q denotes at least one element selected from among C, N, S, P, Si, F, Cl, I and Br; and x, a, b, c and d are within the range of 0xe2x89xa6xxe2x89xa61.1, 0xe2x89xa6axe2x89xa60.5, 0.05xe2x89xa6bxe2x89xa61.0, 0.000001 xe2x89xa6c less than 0.05 and 0xe2x89xa6dxe2x89xa60.1, respectively).
Primary particles (of the order of submicrons) and/or secondary particles (aggregate of primary particles) of said particles are composed of tilting function materials where the multiple oxide Q has a higher density inside than on the surface layer.